Patterned surfaces with suction

ABSTRACT

A microstructured pressure-sensitive surface is described comprising a Wenzel-Cassie hydrophilic-hydrophobic zone structure and capillary action with improved peel strength. The capillary action is enhanced by the Wenzel-Cassie zone creation, and the barrier energy to disruption of the Wenzel-Cassie zone is increased by the capillary action. The micro-structured surfaces of the present invention create water zones of exclusion, where entropic effects reinforce Wenzel-Cassie zone stability, creating a suction effect that conforms the microstructure surface to a target surface.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims benefit of the following patent application(s)which is/are hereby incorporated by reference: U.S. ProvisionalApplication No. 62/711,545 filed on Jul. 29, 2018.

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The copyright owner has noobjection to the reproduction of the patent document or the patentdisclosure, as it appears in the U.S. Patent and Trademark Office patentfile or records, but otherwise reserves all copyright rights whatsoever.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO SEQUENCE LISTING OR COMPUTER PROGRAM LISTING APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

The present invention relates generally to a microstructured adhesivepressure-sensitive surface.

More particularly, this invention pertains to a microstructured adhesivepressure-sensitive surface having a hierarchical structure comprising aWenzel-Cassie and Cassie-Baxter hydrophilic-hydrophobic zone structureand capillary action with improved shear and peel characteristics

Repositionable pressure-sensitive adhesive surfaces are surfaces whichpredictably adhere to, yet remain repeatedly peelable from, a variety oftarget substrates over a long period of time without damaging or marringthe substrate. These adhesive devices may have many commercial uses. Forexample, labels, protective films, and medical surfaces all may be usedto quickly adhere to metal, paper, plastics, and/or skin, but must alsopeel smoothly away from these varied target substrates without leavingbehind any adhesive residue or causing harm or damage to the surface ofthe particular target substrate.

Fundamentally, an understanding of the adhesive effects associated withsuctional hierarchical microstructures is to understand how solutesinteract with hydrophobic and hydrophilic surfaces. Within such aqueouszones, solutes can sense surface features. Sensing interactions aregenerally thought to fall off within nanometers of the surface, althoughin colloidal and biological systems studied in confined spaces,size-dependent depletion effects may extend by up to several particlediameters.

The realization of artificial hydrophobic/hydrophilic surfaces relies ontwo main features: the surface material chemical composition and itsmorphological structure. Usually, the chemical composition is anintrinsic property of materials. On the other hand, micro- andnano-morphology may enhance hydrophobicity/hydrophilicity, especially byexploiting hierarchical and fractal architectures, allowing air pocketformation to create three phase domain zones (liquid/gas/solid).

Hydrophilic-hydrophobic interfaces, such as those developed in theWenzel-Cassie interface state, play a more profound role than generallyassumed. Solutes in aqueous suspension are extensively excluded from thevicinity of many interfaces, and such exclusion arises from long-rangerestriction of water molecules, nucleating at the interface of amacrostructure surface and projecting well into the aqueous phase,similar to what occurs in liquid crystals. The presence of suchunexpectedly large zones of mobility-limited water may impact manyfeatures of surface and interfacial chemistry.

Surface porosity, in addition to hydrophobic and hydrophilicmicrostructures, may play an important role in developing exclusionzones that are robust against thermal and mechanical disruption. Inparticular, surface porosity is important in developing high energeticbarriers to peel disassociation of an interface between amicrostructured surface and a target surface mediated by a liquid. Here,capillary action is introduced as an additional control aspect, having atemporal component and a reinforcing component regarding sheartranslations and peel force.

What is needed, then, is a uniformly coated, unfilled, microstructuredpressure-sensitive adhesive article which exhibits initialrepositionability when adhered to a variety of target substrates.Through the independent variation and selection of microstructuredpatterns and considering the chemical nature of the material comprisingthe microstructured pressure-sensitive article, the applicants havedemonstrated constant or increased long-term adhesion as required bymany applications.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to an article, including adhesive surfacesand transfer coatings, bearing a continuous pressure-sensitive adhesivelayer having a microstructured surface wherein the microstructuredsurface may comprise at least two kinds of features and wherein thelateral aspect ratio of the features may range from about 0.1 to about10 for each feature, and at least one feature dimension difference maybe of at least a factor of 3. In one embodiment, two sets of pillars,one 5 microns in diameter and 30 microns tall and another set of pillars15 microns or greater in diameter and 75 microns tall, may be configuredsuch that the first set of pillars is disposed on the top surface of thesecond set of pillars (i.e., hierarchical). At least two of the featuredimensions (height, width and length) may be microscopic. In someembodiments, all three of the feature dimensions (height, width, length)may be microscopic.

The microstructured patterned adhesive may exhibit initialrepositionability when adhered to a variety of target substrates throughthe independent variation and selection of microstructured pattern andselection of the chemical nature of the microstructured substrate. Themicrostructured pattern may display reduced, constant, or increasedlong-term adhesion as required by the intended application.

In order to satisfy the above needs, understanding the variation of thecontact angle formed between a microstructure surface and a waterdroplet as the surface texture varies may be useful. The conventionalunderstanding is based on chemically homogeneous smooth solid surfaces.Variables such as surface tension of the solid-vapor, solid-liquid, andliquid-vapor interfaces may be important. For a rough hierarchicalsurface air or liquid may remain trapped in the surface asperities.Therefore, a fraction of the sample solid surface may be directly incontact with the droplet total area, while the other fraction may firstcontact an air or liquid layer underneath the droplet. How the interfacestructure develops may depend on the spatial size and distribution ofhydrophobic and hydrophilic regions leading respectively to an airpocket and the precursor liquid film formation between hydrophilic andhydrophobic zones. Wenzel and Cassie-Baxter models may need to beconsidered together to completely describe the wettability of amicrostructured hierarchical surface.

The different microstructure dimensions may not have as much effect onthe apparent contact angle as the texture depth. That is, when themicrostructures are arranged hierarchically, on top of one another, thedistance from the top structure to the base substrate may be animportant determinant of contact angle at discrete positions on themicrostructured surface. On the other hand, the water fractions mayfollow the same trend in contact angle variation as a surface in whichthe various microstructure were placed side by side, and nothierarchically. Therefore, the change in apparent contact angle with thetexture depth may be strongly dependent on the water fraction. Thisobservation suggests an interpretation of this behavior in terms ofcapillary phenomena. Indeed, the adhesive effect of the surface may bedramatically enhanced by adding structures with hollow members, or byplacing perforations in the substrate.

The phenomenon known as capillary rise may be influenced by porosity,and in particular the distribution of the pores. It is known that overcertain length scales, pore surface and volume of most porous media arefractal. Capillary rise may be maximized when the root mean square ofthe pore diameter is between 0.25 and 0.7 of the capillary density. Thisis called the fractal dimension. The formation of Wenzel-Cassie domainsmay also by maximized in this domain. Too many capillaries and theWenzel-Cassie domains may be disrupted, and too few and the peel forcemay diminish rapidly. The exact fractal porosity density to use maydepend on the texture depth, since in some sense the porosity and depthmay accomplish the same function. It should be noted, open pores maymaximize peel force for fractal dimensions on the lower end of the0.25-0.70 range.

In one embodiment of the present invention, a microstructured adhesivepressure-sensitive surface comprised of at least two microstructuredpatterns of different dimensions arranged hierarchically wherein atleast one of the microstructured patterns may be suctional or thehierarchical combinations creates a suctional aspect. A suctional aspectmay be a negative feature that draws fluid away from the target surfacewhen the microstructure adhesive surface is brought in contact with asurface comprising a fluid layer.

In one embodiment of the present invention, a microstructured adhesivepressure-sensitive surface may be comprised of three microstructuredpatterns of different dimensions arranged hierarchically wherein atleast one of the microstructured patterns may be suctional or thehierarchical combinations creates a suctional aspect.

In one embodiment, a substrate layer may comprise a two-dimensionalpattern which is embossed in such a way that both sides of the substratelayer exhibit a sinusoidal aspect. Furthermore, on top of the sinusoidalsubstrate layer may comprise embossed solid cylinders filling eachcomplete square cycle of the sinusoidal pattern with between 10 and 100equally spaced cylinders. Embossed on top of each cylinder in the firstpattern of cylinders may be 1 to 10 solid cylinders of a smallerdimension. The capillary effect may be initiated by placing themicrostructure surface on the fluid layer of the target surface, andapplying a slight pressure to deform the sinusoidal pattern into aflatter conformation, such that when the pressure is removed thesinusoidal aspect may return to its prior sinusoidal shape. This actionmay generate a suctional force in combination with a capillary forcegenerated by the close placement of the pillars.

In one embodiment, the adhesive device may comprise a flat substratelayer. On top of the flat substrate layer is embossed solid cylinders ina uniformly space square array. Embossed on top of each cylinder in thefirst pattern of cylinders may be 1 to 10 solid cylinders of a smallerdimension. The interstitial areas between the first layer of pillars maycomprise drilled cylindrical holes, which may be drilled completely, orpartially, through the substrate layer. The fractal dimension of thedrill holes may be in the range of 0.25 to 0.70. The capillary effectmay be initiated by placing the microstructure surface on the fluidlayer of the target surface without any applied pressure. The firsthierarchical cylinders may draw water away from the target surfacesufficiently such that the water comes into contact with the negativefeatures comprising the drilled holes. The drilled holes may apply asecond capillary effect, which may draw the microstructure layer intointimate contact with the target surface.

One embodiment may consist of a flat substrate layer. Disposed on top ofthe substrate layer may be solid cylinders in a uniformly spaced squarearray. On top of each cylinder in the first pattern of cylinders may bedisposed 1 to 10 solid cylinders of a smaller dimension. Theinterstitial areas between the first layer of pillars may comprisedrilled cylindrical holes from the reverse side of the substrate layer.These reverse drilled holes do not communicate with the first side butstop 5-20 microns before drilling through. On the reverse side,piercings are made that are aligned so as to pierce the centers of thereverse-side drilled holes.

To make the piercing, a perforator, such as a needle, with a 1 to 10micron diameter may be used. The fractal dimension of the drill holesmay be in the range of 0.25 to 0.70. The capillary effect may beinitiated by placing the microstructure surface on the fluid layer ofthe target surface without any applied pressure. The first hierarchicalcylinders may draw water away from the target surface sufficiently suchthat the water comes into contact with the pierced surface of thesubstrate layer. A slight pressure may be applied, the piercings may actas valves and let fluid leave the interface layer through the reversedrilled holes, and not to return.

In one embodiment, the adhesive device may comprise a flat substratelayer. Disposed on top of the substrate layer may be solid cylinders ina uniformly space square array. Disposed on top of each cylinder in thefirst pattern of cylinders may be 1 to 10 solid cylinders of a smallerdimension. In the interstitial areas between the first layer of pillarsmay be an identical array of hollow pillars of the dimensions of thefirst layer of pillars. The fractal dimension of the hollow pillars maybe in the range of 0.25 to 0.70 relative to the solid pillars. Thecapillary effect may be initiated by placing the microstructure surfaceon the fluid layer of the target surface without any applied pressure.The solid hierarchical cylinders may draw water away from the targetsurface in one aspect and the hollow pillars may draw water away fromthe target surface in another capillary aspect.

Hierarchical structures may be constructed commonly. For example, auniform square grid of solid cylinders of varying height, such that saidgroups of solid cylinders form pyramidal structures. In this case, theremay be a first capillary action between adjacent cylinders and a secondcapillary action between the larger formed pyramids. Such a surface mayshift in dominance from one capillary action to another as pressure isapplied, and the fine structure cylinders deform into more or less solidpyramids.

In some embodiments of the present invention, an adhesive surface may becombined with other adhesive techniques. For example, the inclusion of achemical or viscous adhesive may be included. The use of suction cupsthat primarily work by creating a vacuum rather than capillary action.Solid adhesives, such as fiber Gecko structures, that create adhesionbetween the solid of the microstructured surface and a dry surface viavan der Waals forces on a target surface that typically is wet at somelater time.

Some embodiments of the present invention relate to microstructuredsurfaces that are more adhesive when wet or are more adhesive in thepresence of a surfactant or hydrophobic liquid, such as oil. One of thedistinguishing features of the present invention is the enhancement ofWenzel-Cassie effect by combining with capillary action.

The addition of the capillary effect aids in the formation ofhydrophilic and hydrophobic zones, but also supplies a mostly normalforce adhesivity. The Wenzel-Cassie effect and the capillary effectenhance each other's barrier to disruption. The surprising aspect of acapillary Wenzel-Cassie structure is that a mixed interface, for exampleof water and soap, increases both peel force and translational force.For example, adding a lubrication composition to an interface between acapillary Wenzel-Cassie surface and a target surface may increaseadhesivity. Furthermore, aqueous environments may involve bothhydrophobic and hydrophilic components. For example, water-oil emulsionsmay be encountered in many external environments. Water-lipid emulsionsmay be encountered in most biological environments. Even skin to surfaceenvironments, where high humidity is present, may comprisehydrophilic-hydrophobic interfaces. Examples are beverage containers,various skin contacting surfaces such as bandages, and industrialequipment where high grip is required.

The combination of capillary Wenzel-Cassie microstructures surfaces withconventional adhesives is of particular utility, since most conventionaladhesives fail when exposed to oil or soap. Furthermore, a composite ofvisco-adhesive and microstructured adhesive would prevent transientfailures, such as when an article is temporarily exposed to water oralternatively when a normally wet interface becomes dry.

In some embodiments, the adhesivity of the present invention is aneffect that may build over time based on the ordering of molecularconstituents at the microstructure surface target surface interface.There are additional benefits, for example, since surfaces of thepresent invention, especially those surfaces that may be elastomeric,tend to arrange their surface with respect to the target surface.Interfacing with irregular surfaces may require this accommodativeeffect, something seldom experienced with visco-adhesive surfaces, thatstick wherever they first make contact. There may be considerableadvantage in a surface that adheres to another surface in a way thattheir interface may not result in localized stresses, wrinkles, orfolds.

In one embodiment of the present invention, the variation of attributesacross a surface may be utilized. In some regions shear translations maybe prevented, and in other regions peel translations may be prevented,and in still other regions both effects may be required. More broadly,it may be desired in some regions that shear translations are to bepromoted with minimal force, and still other regions the peel force tobe minimized.

One embodiment of the present invention may comprise a microstructuredadhesive pressure-sensitive surface comprised of at least twomicrostructured patterns of different dimensions arranged hierarchicallywherein at least one of the microstructured patterns is suctional or thehierarchical combinations creates a suctional aspect. A suctional aspectmay comprise a negative feature that draws fluid away from the targetsurface when the microstructure adhesive surface is brought in contactwith a surface comprising a fluid layer. The combination of the twopatterns may create a zone of exclusion, characterized bymicrostructured water.

In some embodiments, an adhesive device may comprise a substrate layeronto which is embossed a two-dimensional pattern in such a way that bothsides of the substrate layer exhibit a sinusoidal aspect. Furthermore,on top of the sinusoidal substrate layer is embossed solid cylinders(for example, micropillars) filling each complete square cycle of thesinusoidal pattern with between 10 and 100 equally spaced cylinders. Ontop of each cylinder in the first pattern of cylinders is embossed 1 to10 solid cylinders (for example, micropillars) of a smaller dimension.Wherein the first and second layers of pillars create a zone ofexclusion, and a microstructured water state. The capillary effect isinitiated by placing the microstructure surface on the fluid layer ofthe target surface, and applying a slight pressure to deform thesinusoidal pattern into a flatter conformation, such that when thepressure is removed the sinusoidal aspect returns to its priorsinusoidal shaping generating a suctional force in combination with acapillary force generated by the close placement of the pillars.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an illustration of a microstructured molding tool.

FIG. 2 is an illustration of a microstructure printing tool.

FIG. 3a is an illustration of a microstructure molding tool and printingtool being used together.

FIG. 3b is cross-sectional view of a microstructure adhesive capillarystructure demonstrating gas/liquid interfaces.

FIG. 4 is a diagram of cross-sectional views of various wettinginterfaces between a surface and liquid/gas.

FIG. 5 is a cross-sectional view of an interface between a 2-tiermicrostructure surface and liquid/gas.

FIG. 6 is a cross-sectional view of an interface between a 1-tiercapillary microstructure and liquid/gas.

FIG. 7 is a cross-sectional view of an interface between a 1-tiercapillary microstructure and liquid/gas.

FIG. 8 is a top view of a multi-tier microstructured surface.

FIG. 9 is a cross-sectional view of a pyramidal microstructure.

FIG. 10 is a top view of an interlocking geometry microstructure.

FIG. 11 is a top view of interlocking microstructured surfaces.

FIG. 12 is a perspective view of an adhesive device comprising threemicrostructured patterns.

FIG. 13 is a cross-sectional view of an adhesive device comprising threemicrostructured patterns and capillaries.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the embodiments of the presentdisclosure, one or more examples of which are set forth herein below.Each embodiment and example is provided by way of explanation of thedevice, composition, and materials of the present disclosure and is nota limitation. Rather, the following description provides a convenientillustration for implementing exemplary embodiments of the disclosure.In fact, it will be apparent to those skilled in the art that variousmodifications and variations can be made to the teachings of the presentdisclosure without departing from the scope or spirit of the disclosure.For instance, features illustrated or described as part of oneembodiment, can be used with another embodiment to yield a still furtherembodiment. Thus, it is intended that the present disclosure covers suchmodifications and variations as come within the scope of the appendedclaims and their equivalents. Other objects, features, and aspects ofthe present disclosure are disclosed in or are obvious from thefollowing detailed description. It is to be understood by one ofordinary skill in the art that the present discussion is a descriptionof exemplary embodiments only and is not intended as limiting thebroader aspects of the present disclosure.

In order to overcome the problems of the prior art, understanding thevariation of the contact angle formed between a microstructure surfaceand a water droplet as the surface texture varies is needed. Theconventional understanding is based on chemically homogeneous smoothsolid surfaces. The important variables are surface tensions of thesolid-vapor, solid-liquid, and liquid-vapor interfaces. For a roughhierarchical surface, air or liquid may remain trapped in the surfaceasperities. Therefore, a fraction of the sample solid surface isdirectly in contact with the droplet total area, while the otherfraction will first contact an air or liquid layer underneath thedroplet. How the interface structure develops depends on the spatialsize and distribution of hydrophobic and hydrophilic regions leadingrespectively to an air pocket and the precursor liquid film formationbetween hydrophilic and hydrophobic zones. Wenzel and Cassie-Baxtermodels need to be considered together to completely describe thewettability of a microstructured hierarchical surface.

It was known in the art that a combination of microstructured patternand rheological properties may provide a means of producingpressure-sensitive adhesive layers of tapes and transfer coatings. Theapplicants have found that a combination of microstructured pattern andWenzel-Cassie characteristics provide an improved pressure-sensitivemicrostructured adhesive surface.

Methods of Making Microstructured Surfaces

The depiction in FIG. 1 involves the use of a microstructured moldingtool 100 to emboss a hierarchically arranged microstructure layer of apressure-sensitive adhesive surface 102 having a planar surface 104 andfirst 106 and second 108 microstructures. The thickness of themicrostructure layer 110 which is embossed by such microstructuredmolding tool 112 can vary depending upon the requirement of the finalapplication. The microstructured layer 110 must be thick enough suchthat after embossing, a continuous unbroken microstructured surface 114is obtained. Typically, the microstructured layer 110 is formed at athickness of about 10 μm to about 250 μm, preferably about 50 to about150 μm. In some embodiments, the thickness is 100 μm. Themicrostructured molding tool 112 is applied by rolling through flatstock 116, at a sufficiently slow rate and at a sufficient temperatureand pressure to impart the desired features to provide a continuousmicrostructure layer 114 having a microstructured surface 110 (typicallyabout 0.1 second to about 5 minutes at a temperature of about 20° C. toabout 150° C.) depending on the materials and microstructure surfacedesired. The sample is allowed to cool on a flat surface, yielding amicrostructured pressure-sensitive surface 114 which substantiallyreplicates the shaping and pattern of the particular microstructuredmolding tool 112.

The second method illustrated by FIG. 2 involves printing a layer ofpressure-sensitive microstructure 200 onto a flat substrate layer 202using a microstructure printer 204. The structure 200 can be formed by adot matrix printer which may print spheres 206 in a liquid state suchthat when deposited in succession touching dots fuse 208, and dots incontact 210 with substrate 202 fuse. After printing, the finishedproduct may be allowed to cure or solidify on a flat surface. Atwo-dimensional array of hierarchical structures can be formed in thisway.

The third method illustrated by FIG. 3 involves the embossing of a firstmicrostructure 304 followed by the printing of a second microstructure310. This method involves the use of a microstructured molding tool 302to emboss a layer of hierarchically arranged microstructure of apressure-sensitive adhesive surface having a planar surface 306 andfirst 304 microstructure. A second microstructure layer 310 is printed308. The thickness of the microstructure layer 312 can vary dependingupon the requirement of the final application. The microstructured layer312 may be thick enough such that after forming a continuous, unbrokenmicrostructured surface 314 is obtained. Typically, the microstructuredlayer is formed at a thickness 312 of about 10 μm to about 250 μm,preferably about 50 to about 150 μm. The microstructured molding tool302 may be applied by rolling through flat stock 316, at a sufficientlyslow rate and at a sufficient temperature and pressure to impart thedesired features to provide a continuous microstructure layer 314 havinga micro structured surface 304 (typically about 0.1 second to about 5minutes at a temperature of about 20° C. to about 150° C.) depending onthe materials and microstructure surface desired. The sample is allowedto cool on a flat surface prior to the printing step, yielding amicrostructured pressure-sensitive surface 316 which substantiallyreplicates the shaping and pattern of the particular microstructuredmolding tool 302.

Microstructured Molding Tools

A microstructured molding tool is an implement for imparting a structureto planar, flat feedstock, and which may be continuously reused in theprocess. Microstructured molding tools can be in the form of a planarstamping press, a flexible or inflexible belt, or a roller (as depictedin FIGS. 1 and 2). Furthermore, microstructured molding tools aregenerally considered to be tools from which the microstructured adhesivepattern is generated by embossing, coating, casting, or platen pressingand do not become part of the finished microstructured adhesive article.

A broad range of methods are known to those skilled in this art forgenerating microstructured molding tools. Examples of these methodsinclude but are not limited to photolithography, etching, dischargemachining, ion milling, micromachining, and electroforming.Microstructured molding tools can also be prepared by replicatingvarious microstructured surfaces, including irregular shapes andpatterns, with a moldable material such as those selected from the groupconsisting of crosslinkable liquid silicone rubber, radiation curableurethanes, etc. or replicating various microstructures by electroformingto generate a negative or positive replica intermediate or finalembossing tool mold.

Microstructured molds having random and irregular shapes and patternscan be generated by chemical etching, sandblasting, shot peening orsinking discrete structured particles in a moldable material.Additionally, any of the microstructured molding tools can be altered ormodified according to the procedure taught in Benson U.S. Pat. No.5,122,902. Finally, the microstructured molding tool must be capable ofseparating cleanly from the pressure-sensitive adhesive layer.

Microstructured Materials

Typically, the microstructured surfaces are made from materials selectedfrom the group consisting of embossable or moldable materials havingsufficient structural integrity to enable them to withstand the processof conveying the microstructure to the adhesive and be cleanly removedfrom the microstructured adhesive layer. Preferred materials which themicrostructured surface may comprise include but are not limited tothose selected from the group consisting of plastics such aspolyethylene, polypropylene, polyesters, cellulose acetate,polyvinylchloride, and polyvinylidene fluoride, as well as paper orother substrates coated or laminated with such plastics.

Embossable coated papers or thermoplastic films are often siliconized orotherwise treated to impart improved release characteristics. As notedin the discussions of methods for making the surfaces of the presentinvention, depending on the method employed and the requirements of thefinal article, one or both sides of these surfaces must have releasecharacteristics. For example, embossing can include a rollerconfiguration in which one roller is a positive form and the otherroller is a negative form, which mate together into forming the embossedsurface as the planar feedstock is passed the embossing rollers.

Features of Microstructured Surfaces

The microstructured molding tools, feedstock, and, ultimately, themicrostructured pressure-sensitive microstructured surfaces of thepresent invention have a multiplicity of projection features. The term“projection feature” as used herein covers both negative and positiveconfigurations providing microstructured surfaces with positive andnegative configurations, respectively. These features are commonlyreferred to as negative or positive structures by those who are familiarin the art of microstructured technology. Each feature should ortypically have a height of about 2.5 micrometers to about 375micrometers, preferably about 25 micrometers to about 250 micrometers,and most preferably about 50 micrometers to about 150 micrometers forreasons of minimizing thickness of the surface, increasing the densityof the microstructured adhesive pattern sizes for symmetric patterns,and controlling the placement of microstructure levels.

The shape of the features in the microstructured molding tool and themicrostructured pressure-sensitive microstructured articles preparedtherefrom can vary. Examples of feature shapes include but are notlimited to those selected from the group consisting of hemispheres,prisms (such as square prisms, rectangular prisms, cylindrical prismsand other similar polygonal features), pyramids, ellipses, and grooves.Positive or negative features can be employed, i.e. convex hemispheresor concave hemispheres, respectively. The preferred shapes include thoseselected from the group consisting of cylinders, sinusoids, hemispheres,pyramids (such as cube corners, tetrahedra, etc.), and “V” grooves, forreasons of pattern density, adhesive performance, and readily availablemethodology of the micro structured pattern generation or development.Although the exemplified features are non-truncated in nature, it isbelieved that truncated features will also be suitable in the articlesof the present invention. The features of the microstructured surfacemay be systematically or randomly generated.

The limits of lateral dimensions of the features can be described by useof the lateral aspect ratio (LAR) which is defined as the ratio of thegreatest microscopic dimension of the feature parallel to the plane ofthe continuous layer of feedstock to either the height of a positivefeature or depth of a negative feature. Too large LAR leads to a shortsquat feature that would not provide the advantages of microstructuring.Too small a LAR would lead to a tall narrow feature which would notstand upright due to the low flexural modulus of the many elastomericpolymers (and therefore low flexural rigidity of the feature). That is,typical elastomers will not support too small a LAR whereas too large aLAR will not achieve the needed Wenzel-Cassie structure obtained fromhierarchical placement of the microstructures. Typical limits of the LARwould be about 0.1 to about 10, with most preferred limits of about 0.2and about 5.

The nearest neighbor distance between features can be specified with aspacing aspect ratio (SAR) given by the ratio of center-to-centernearest neighbor distance to feature the greatest lateral microscopicdimension as defined for the LAR. The minimum value the SAR can assumeis 1 which corresponds to the sides of features touching. This value ismost useful for features such as hemispheres and pyramids. For featuressuch as rods, square prisms, rectangular prisms, inverted cones,hemispheres, and pyramids, the SAR should be greater than 1 so that theperimeters of the top of the features do not touch and so form a newplanar surface. A typical upper limit for the SAR would be 5 and a moredesirable upper limit would be 3. A most preferred upper limit would be2.5. Although the precise arrangement of microstructures is stronglymaterial dependent.

If the SAR is too great, positive features may not be able to supportthe hydrophilic phase of the interface layer of fluid above thesubstrate surface. This leads to disruption of the desired Wenzel-Cassieinterface of contact between the microstructure surface and targetsurface. That is, the microstructure comprising the flat regions betweenpositive features would touch the target surface. In either case ofpositive or negative features, carried to an extreme, a large SAR wouldlead to essentially a planar surface of contact. A pattern withasymmetry could be defined by multiple SARs. In the case of multipleSARs, all SARs should obey the limits listed above.

Reentrant Microstructures

Multiscale features and hierarchical arrangement may be used to producecapillary-enhanced adjacent hydrophobic-hydrophilic zones on amicrostructured surface. When such a surface comes in contact with afluid layer on a target surface, a Wenzel-Cassie interface may formwhich may be comprised of microscopic regions of hydrophilic fluidsurrounded by microscopic regions of hydrophobic fluid or gas. One zonetraps the other zones, which may result in high shear forces. Incombination with capillary action, peel forces may also be enhanced.

If the surface energy difference between the hydrophobic zone and thehydrophilic zone is sufficient, then the water in the hydrophilic zonemay become structured, resulting in a further increase in the barrierenergy to disruption of the zones. In one embodiment, the formation ofstructured water may not be required for the present capillary enhancedWenzel-Cassie zones, but in other embodiments it may be a preferredstate, wherein extremely high peel strengths may be obtained.

In some embodiments, the contact between a microstructured surface ofthe present invention and a target surface comprises a three-phase line(e.g., liquid/solid/gas). If a portion of the microstructured surface isconcave (re-entrant), then the three-phase interface may be more stable.

For example, a surface pattern may be built of small holes upon largerscale grooves, the holes may trap air and promote large contact angle,whereas larger grooves are filled by water and may prevent watersliding. The opposite situation may also occur, when small holes may bewetted while larger ones hold air pockets. Under some circumstances aCassie-Baxter to Wenzel partition may be caused by small vibration.

The stability of the Cassie-Baxter state for different shapes ofroughness patterns may depend on the potential barrier separating theCassie-Baxter and Wenzel states. The different shapes may includespheres and spherical cavities, pillars with changing cross section(overturned cones) and with side facets. For hydrophobic surfaces, themultiscale roughness may increase the potential barrier for the wettingtransition. In some embodiments, inherently hydrophilic materials mayappear hydrophobic when the energy gain due to the wetting of ahydrophilic pore is overcompensated by the energy loss due to the growthof a water-air interface. This can lead to the apparent hydrophobicityof an inherently hydrophilic material when an appropriate pattern isintroduced. The potential energy barriers to the conversion ofCassie-Baxter to Wenzel state transition may be created due to wideningof the gap between the posts while if a capillary effect is present thenthe liquid-air front propagates. This may increase the liquid-airinterface area and, therefore, the net energy term may be proportionalto the liquid-air interfacial area times the surface tension of theliquid.

The concave topography may be particularly significant for theoleophobicity involving the resistance to wetting by low interfacialenergy liquids, such as non-polar organic oils and hydrocarbons. TheWenzel state may not enhance liquid repellent for such materials, whilethe Cassie-Baxter state may tend to be unstable. Therefore, re-entrantsurface topography may be used for the surface's oleophobicity, since itis capable of pinning the liquid-air interface and stabilizing theCassie-Baxter state. In one embodiment, the double reentrant topographycan further enhance the stabilizing effect even for extremely lowsurface tension liquids.

Capillary Structures with Hydrophobic Surface

In some embodiments, a larger structure which is capillary attractivemay be stabilized by making the inner capillary surface hydrophobic.This may impart an irreversible capillary effect. A liquid dropletplaced on a geometrically textured surface may take on a “suspended”state, in which the liquid wets only the top of the surface structure,while the remaining geometrical features are occupied by vapor. Thissuperhydrophobic Cassie-Baxter state may be characterized by itscomposite interface, which is intrinsically fragile and, if subjected tocertain external perturbations, may collapse into the fully wet Wenzelstate.

It should be noted that the hydrophobicity at one scale may inherit asimilar propensity on a larger scale. The concept of hierarchicalsurface structures for perpetual superhydrophobicity can be illustratedby a micrometer scale, which realizes a perpetual nano-Cassie-Baxterstate, and the other on the structure with a 10-micrometer (or larger)scale, which inherits the stability of the smaller scale. The perpetualsuperhydrophobicity may be obtained with the complete thermodynamicelimination of the Wenzel state. By utilizing hierarchical surfacestructures, which exploit the perpetual superhydrophobicity of themicron-scale textures, in combination with the wedge drying phenomenonat larger scales, one may obtain this superhydrophobicity.

Water/Oil Interfaces Under Capillary Action

A tube comprised of a hydrophobic material may have a negative capillaryrise, that is the level of water in the tube when pressed into the waterwill be lower than the surrounding water surface. A tube comprised of ahydrophilic material may have a positive capillary rise, that is thelevel of water in the tube is higher than the level of the watersurrounding the tube. Hence, using this difference, one may usecapillaries of different hydrophilicity to control the equilibriumbetween hydrophilic Wenzel zones and hydrophobic Cassie zones.Capillaries in a microstructured surface can determine Cassie to Wenzeltransitions, or support the stability of a Wenzel-Cassie equilibriumbetween two zones, one in the Wenzel state and the other in the Cassiestate.

There are four distinct phenomena regarding microlines and the evolutionof an oil-air/water interface between two neighboring microlines duringcapillary action on water droplets. First, when a water dropletgradually shrinks, the oil-air/water interface between two neighboringmicrolines increased its deflection but decreased its angles with thesidewalls of these two microlines. The two edges of this interface arestill at the top corners of the two microlines. Once water passes thetop corners of these two microlines, it keeps moving down and fillingthe gap between the two microlines. Third, as the water droplet shrinks,the number of microlines on which the droplet sits also decreases. Thegaps between microlines might not be filled spontaneously by water whentransition occurs. Instead, it is more likely the gaps between themicrolines are filled incrementally. The pressure may not be uniforminside the droplet or the microlines may not be exactly identical.Either cause leads to the occurrence of filling phenomena.

Referring now to FIG. 3b , a cross-section view of a microstructureadhesive capillary structure 350 with an air/water interface 352 betweentwo neighboring microlines. The intrinsic contact angle 354 with amicroline and the angle 356 between the advancing angle and the verticalare also shown.

Water/Surfactant Interfaces Under Capillary Action

In some embodiments, surfactants may be compounds that lower the surfacetension (or interfacial tension) between two liquids, between a gas anda liquid, or between a liquid and a solid. Surfactants may act asdetergents, wetting agents, emulsifiers, foaming agents, anddispersants. The applicants have surprisingly discovered thatsurfactants that generally lubricate an interface increases theresistance to shear translation and peel force when at least one of thesurfaces is a microstructured surface. It was found that surfactantsreinforce the boundaries between Wenzel and Cassie phases, thus phaselock the interface. Surfactants may be particularly useful on targetsurfaces that are coated with a high viscosity liquid.

In the bulk aqueous phase of an interface, surfactants may formaggregates, such as micelles, where the hydrophobic tails form the coreof the aggregate and the hydrophilic heads are in contact with thesurrounding liquid. These micelles may align along the surfaces betweenhydrophobic regions and hydrophilic regions of the microstructuredadhesive surface. Other types of aggregates can also be formed, such asspherical or cylindrical micelles or lipid bilayers. These lipidbilayers can be associated with microstructured surfaces in which thepitch is varying. The shape of the aggregates may depend on the chemicalstructure of the surfactants. In some embodiments the structure maydepend on the balance in size between the hydrophilic head andhydrophobic tail, as well as the height, diameter and pitch of themicrostructures. Surfactants may also reduce the surface tension ofwater by adsorbing at the liquid-air interface. This effect may reducecapillary rise.

The dynamics of surfactant adsorption may affect the adhesive propertiesof a microstructured surface. In some embodiments, surfactants canstabilize the adhesive boundaries between hydrophilic and hydrophobiczones in the interface, a Wenzel-Cassie structure, if there is a flowcondition. For example, where bubbles or drops are rapidly generated bythe target surface and need to be stabilized surfactants may beutilized. The dynamics of adsorption depend on the diffusion coefficientof the surfactant. As the interface is created, the adsorption islimited by the diffusion of the surfactant to the interface. In someembodiments, there can exist an energetic barrier to adsorption ordesorption of the surfactant. This may be the case when the surfactantenhances either translational grip or peel grip. If such a barrierlimits the adsorption rate, the dynamics may be ‘kinetically limited’.Such energy barriers may be due to steric or electrostatic repulsions.The surface rheology of surfactant layers, including the elasticity andviscosity of the layer, may play an important role in the stability ofWenzel-Cassie structures in an interface between a microstructuredsurface and a target surface.

The surfactant may be applied selectively to the microstructuredsurface, for example on the top (smallest) features, or in the valleysof the largest features. The surfactant may be applied as a liquidcoating or a solid coating.

Surfactants may include soaps obtained by treating vegetable or animaloils and fats with a strong base, linear alkylbenzenesulfonates, ligninsulfonates, fatty alcohol ethoxylates, and alkylphenol ethoxylates.

The “tail” of most surfactants may be fairly similar, consisting of ahydrocarbon chain, which can be branched, linear, or aromatic.Fluorosurfactants have fluorocarbon chains. Siloxane surfactants havesiloxane chains. Many important surfactants include a polyether chainterminating in a highly polar anionic group. The polyether groups oftencomprise ethoxylated sequences inserted to increase the hydrophiliccharacter of a surfactant. Polypropylene oxides, conversely, may beinserted to increase the lipophilic character of a surfactant.Surfactant molecules may have either one tail or two; those with twotails are said to be double-chained.

Surfactants may be classified according to the composition of theirhead: nonionic, anionic, cationic, amphoteric. A non-ionic surfactanthas no charged groups in its head. The head of an ionic surfactantcarries a net positive, or negative charge. If the charge is negative,the surfactant is more specifically called anionic; if the charge ispositive, it is called cationic. If a surfactant contains a head withtwo oppositely charged groups, it is termed zwitterionic.

Anionic surfactants contain anionic functional groups at their head,such as sulfate, sulfonate, phosphate, and carboxylates. Prominent alkylsulfates include ammonium lauryl sulfate, sodium lauryl sulfate, and therelated alkyl-ether sulfates sodium laureth sulfate, and sodium myrethsulfate.

Cationic surfactants include permanently charged quaternary ammoniumsalts: Cetrimonium bromide, Cetylpyridinium chloride, Benzalkoniumchloride, Benzethonium chloride, Dimethyldioctadecylammonium chlorideand Dioctadecyldimethylammonium bromide.

Zwitterionic surfactants have both cationic and anionic centers attachedto the same molecule. The cationic part is based on primary, secondary,or tertiary amines or quaternary ammonium cations. The anionic part canbe more variable and include sulfonates, as in the sultaines3-[(3-Cholamidopropyl) dimethylammonio]-1-propanesulfonate andcocamidopropyl hydroxysultaine. Betaines such as cocamidopropyl betainehave a carboxylate with the ammonium. The most common biologicalzwitterionic surfactants have a phosphate anion with an amine orammonium, such as the phospholipids phosphatidylserine,phosphatidylethanolamine, phosphatidylcholine, and sphingomyelins.

Nonionic surfactants have covalently bonded oxygen-containinghydrophilic groups, which are bonded to hydrophobic parent structures.The water-solubility of the oxygen groups is the result of hydrogenbonding. Hydrogen bonding decreases with increasing temperature, and thewater solubility of nonionic surfactants therefore decreases withincreasing temperature. Nonionic surfactants are less sensitive to waterhardness than anionic surfactants. The differences between theindividual types of nonionic surfactants are slight. They include:ethoxylates, Fatty alcohol ethoxylates (narrow-range ethoxylate,octaethylene glycol monododecyl ether, pentaethylene glycol monododecylether), Alkylphenol ethoxylates (Nonoxynols, Triton X-100), Fatty acidethoxylates, Special ethoxylated fatty esters and oils, Ethoxylatedamines and/or fatty acid amides (Polyethoxylated tallow amine, Cocamidemonoethanolamine, Cocamide diethanolamine), Terminally BlockedEthoxylates (Poloxamers), Fatty Acid Esters of Glycerol (Glycerolmonostearate, Glycerol monolaurate), Fatty Acid Esters of Sorbitol(Sorbitan monolaurate, Sorbitan monostearate, Sorbitan tristearate),Tweens, Fatty Acid Esters of Sucrose, Alkyl Polyglucosides (Decylglucoside, Lauryl glucoside, Octyl glucoside), Amine oxides, Sulfoxides,Phosphine oxides.

FIG. 4 illustrates an embodiment of Wenzel-Cassie and Cassie-Baxtercapillary wetting surfaces 401. The surface 401, a first microstructure403, a second microstructure 405, and a hydrophilic liquid 407 aredepicted. Adopting the convention that the first mentioned term refersto the wetting state of the first microstructure and the secondmentioned term refers to the wetting state of the second microstructure,then 401 depicts a Cassie-Cassie wetting state (also referred to as aCassie-Baxter state). Referring to 408, the wetting state depicted is aWenzel-Cassie wetting state. Referring to 409, the wetting statedepicted is a Wenzel-Wenzel wetting state. Referring to 411, ahydrophilic surface 413 may create a positive capillary effect in agenerally Wenzel-Wenzel wetting state where air 417 is trapped. However,in 411 the trapped air 417 comprises a Wenzel-Cassie state, and in thisgeometry may be adhesive. Referring to 419, hydrophobic surface 421 maycreate a negative capillary effect in a generally Wenzel-Cassie wettingstate where air 425 is trapped. Notice in 411 the meniscus 415 is convexand in 419 the meniscus 423 is concave. Referring to 427, the wettingstate depicted is a Cassie-Wenzel wetting state, which includes trappedair 429. Referring to 431, generally the wetting state depicted isWenzel-Cassie, where a hole 433 is disposed in the substrate. Thesubstrate of the microstructured surface may comprise a top layer andbottom layer with an interior disposed therein. The hole 433 may bedisposed within the interior and connect to the top surface, bottomsurface, or both. The substrate of the microstructured surface may behydrophilic, and hence the meniscus 435 is convex. Note in 431, thecapillary action of hole 433 has created a downward pressure that hascaused the top second microstructure 437 to be in a Wenzel state.Referring to 439, generally the wetting state depicted is Cassie-Wenzel,where a hole 441 is disposed in the substrate's interior and connectedto the top surface, bottom surface, or both. The substrate of themicrostructured surface may be hydrophilic, and hence the meniscus 435is convex. Note in both 431 and 439, the local interfaces may evolveover time. For example, in 431, second microstructure 437 may have begunin a Cassie state and evolved into a Wenzel state. In 439, the secondmicrostructure 443 is fully wetted and acts as a conduit to hole 441past the trapped air 445.

It will be obvious to those skilled in the art that more elaboratewetting states would be obvious for a three-tier microstructure asdepicted. For example, some embodiments may include holes disposed inthe pillars. For example, the pillars may have an exterior and interiorwith a hole or depression extending from the exterior into the interior.If a hydrophilic liquid such as water comes in contact with ahydrophilic lined hole the water may be caused to flow into the hole. Ifa hydrophilic liquid such as water comes in contact with a hydrophobiclined hole the water my be caused to resist flowing into the hole, ormore generally the hole may anchor a trapped air bubble. Consequently,holes can act as local zones of influence, making surrounding structuresWenzel wetting when the surrounding structures without the hole areCassie wetting, or conversely. Indeed, the time evolution that ischaracteristic of Wenzel-Cassie capillary wetting states is one of thedistinguishing features of these microstructures. While capillary actionmay exist between solid cylinders, as illustrated in FIG. 4, the morecommon capillary action may be associated with cylindrical voids, andmore generally with depressions.

In one embodiment, a capillary structure of use in the present inventionmay include the 2-tier microstructure depicted in FIG. 5. In a 2-tiermicrostructure, the microsurface 500 may comprise a microstructure 503that has an exterior 505 and an interior 507, wherein a hole ordepression 509 may extend from the exterior to the interior. FIG. 5identifies a microsurface 500 that is depicted with reference to liquidinterface 502. Another way to describe the microstructured surface 500includes the microsurface comprised of first microstructure 504, secondmicrostructure 506, and capillary structure 508 (depicted as acylindrical hole). Capillary action is shown by arrow 510. The wettingstate 512 may be a Cassie-Cassie state. The wetting state 514 may be aWenzel-Cassie capillary state. The wetting state 516 may be aWenzel-Wenzel capillary state. State 512 may not be adhesive, and state514 may be adhesive. In some embodiments, if adjacent cells do notpossess holes (capillary structure) 508, then they will be Cassie-Cassie512, and intermediate cells with holes 508 may eventually becomeWenzel-Wenzel 516 (depending on the substrate 520 material), then thetotal wetting state is Cassie-Cassie-Wenzel-Wenzel, which can be highlyadhesive, depending on the surface energy of the liquid phase.

In another embodiment of the present invention, a capillary structuremay include the 1-tier microstructure as depicted in FIG. 6.Microstructure 600 is depicted with reference to liquid interfaces 602.The microstructured surface 600 is comprised of first microstructure 604and capillary structure 606 (depicted as a cylindrical hole). If thecapillary structure 606 is absent the surface wetting is described by602, which can be considered an adhesive Cassie state. When capillarystructure 606 is present then the interface is 608, and is considered aCassie capillary state, which is considerably more adhesive.

In yet another embodiment of the present invention, a capillarystructure may include the 1-tier microstructure depicted in FIG. 7.Microstructure 700 is depicted with reference to liquid interface 702.The microstructured surface is comprised of first microstructure 704which acts also as a capillary structure (depicted as a spherical pore).

Capillary structure that has one side open to the ambient atmosphere mayhave stronger capillary action because the motion of fluid into thecapillary structure is not resisted by the work required to compress agas in a capillary structure that is not open to the ambient atmosphere.Structures that have recurvature, as illustrated in FIGS. 6 and 7 arecalled reentrant microstructures.

Referring now to FIG. 8, an embodiment depicts a birds-eye-view of amulti-tier microstructured surface 800, which may be comprised oflatitudinal ridges 801, longitudinal ridges 802, cylinders 804, andtargets 806. Cylinders 804 comprise two or more latitudinal throughholes 808 and longitudinal through holes 810 such that each set of holes808, 810 are not at the same height and they do not communicate (orintersect). The cylinders 804 may comprise a diameter in the range of 10to 50 microns, height of between 10 to 150 microns, pitch between 20 and200 microns, and may have a second tier of smaller cylinders disposed onthe top portion of the cylinder (not pictured). The targets 806 may becomprised of tiered columns, wherein the the tiers comprise a diameterin the range of 10 to 50 microns, height of between 10 to 150 microns,and pitch between 20 and 200 microns. The latitudinal ridges 801 andlongitudinal ridges 802 may comprise a thickness between 5 to 50microns, height between 2 and 150 microns, and pitch between 5 and 50microns with the dimensions being determined within each of the regions812 and 814. The through holes 808 and 810 may be any profile, includingcircular, oval, rectangular, star, a polygon, or any other shapesuitable for the flow of a liquid, gas, or solid state. The throughholes may be oriented such that 808 aligns with 802 and 810 aligns with801.

The mechanism of action of microstructure surface 800 may be capillary.Capillary action may occur between the ridges of 812 and 814. Thecapillary action from one segment 812, 814 may connect to anothersegment 816, 818 (respectively) via the capillary action of throughholes 808 and 810. The targets 806 may also have capillary action buttheir primary purpose is to gradually link longitudinal flow vectors tolatitudinal flow vectors. A complicated structure as depicted in FIG. 8may take several minutes to equilibrate to its lowest energy state (mostadhesive). This temporal feature of the microstructured surface 800interface with a liquid may be advantageous over the prior artapplications where frequent repositioning of the microstructured surfacewith respect to a target surfaces is anticipated. Microstructuredsurfaces such as 800 comprising target structures 806 may be locked totheir target surfaces by applying a slight normal force, which may placethe target surfaces 806 into a suctional state.

Another embodiment of a microstructured surface that operates similarlyto the structure depicted in FIG. 8 may be constructed by filling inthrough holes 808 and 810 and populating the side surfaces of cylinders808 with microstructures, similar to those previously depicted in FIG.4. In such an embodiment, fluid may flow from longitudinal ridges 802,around the microstructures on 808 and into latitudinal ridges 801.

It should be understood that the embodiments provided in FIGS. 4-8 arehighly symmetric depictions. In many self-organizing systems, and inbiological systems generally, dimensions are only approximatelymaintained. Consequently, the surprising aspects of the inventivemicrostructured surfaces do not rely on a high degree of symmetry andmay work according to their intended purpose when dimensions such asdiameter, height and pitch vary over the surface of the microstructuredsurface. There may be certain advantages to be realized in varying thesedimensions periodically, such that the periodical variation may becomean advantageous structure in itself. For example, a uniform grid ofsolid cylinders like that of the prior art may be given a larger scalemicrostructure by varying their amplitude. Such variations may includesinusoidal, rectangular, pyramidal, and the like structures.

In appreciation of the above observation, the applicants define aself-similar microstructured surface as an at least 2-tiermicrostructured surface comprising now a first microstructure that issmaller in dimension than a second microstructure, such that the firstmicrostructure is of small dimensions, but a second microstructure isformed by spatially shaping a multiplicity of the first microstructures.These self-similar structures have enhanced capillary action.

Referring now to FIG. 9, microstructures surface 900 may be comprised ofsolid cylinders 902 arranged in a pyramidal geometry 904. The pyramidalgeometry 904 may be comprised of cylinders 902 with a constant pitch ofbetween 20 to 100 microns depicted at 906, a diameter of between 10 to100 microns depicted at 908, and a pyramidally varying height. Thepyramidal geometry 904 can be disposed in a two-dimensional gridcomprising pitch 910.

Referring to FIG. 10 is a birds-eye-view, and one embodiment of aninterlocking geometry 1000 which may be comprised of pillars oftriangular cross section 1002 and a central pillar 1004 of star crosssection. Repetitions of these interlocking patterns may be employed inany self-similar microstructure. Generally, any microstructure asexemplified by the embodiments of FIGS. 4-10 may be sculpted into asecond higher dimensional microstructure.

Alternatively, there are many biological structures that exhibit highcapillary activity, similar to that as illustrated in FIG. 10, whereradial capillary action distributes to a square matrix. The regular gridof microstructure incorporating amorphous capillary microstructure maybe especially useful regarding adhesion to target surfaces that areheterogenous. For example, in one embodiment an interface comprised ofwater and oil, or water and soap, or any interface where one phase isresponsive to capillary action and another phase is responsive toWenzel-Cassie organization may benefit from an amorphous capillarymicrostructure.

Referring now to FIG. 12, a microstructured adhesive pressure-sensitivesurface 1200 may be comprised of three microstructured patterns ofdifferent dimensions arranged hierarchically wherein at least one of themicrostructured patterns is suctional or the hierarchical combinationscreates a suctional aspect. In one embodiment, the structure consists ofa substrate layer 1202 onto which is embossed a two-dimensional patternin such a way that both sides of the substrate layer may exhibit asinusoidal pattern 1204 and 1206. Furthermore, on top of the sinusoidalpattern 1204, 1206 is embossed solid cylinders (for example,micropillars) 1208 filling each complete square cycle 1210 of thesinusoidal pattern with between 10 and 100 equally spaced cylinders. Ina hierarchical fashion, on top of each cylinder 1208 in the firstpattern of cylinders is embossed 1 to 10 solid cylinders (for example,micropillars) 1214 of a smaller dimension. The capillary effect may beinitiated by placing the microstructure surface on the fluid layer 1216of the target surface, and applying a slight pressure 1218 to deform thesinusoidal pattern into a flatter conformation 1228, such that when thepressure is removed the sinusoidal aspect returns to its priorsinusoidal shaping 1204, 1206 generating a suctional force 1222 incombination with a capillary force 1224 generated by the close placementof the cylinders 1208.

Referring now to FIG. 13, an embodiment of the present invention may bea microstructured adhesive pressure-sensitive surface comprised of threemicrostructured patterns of different dimensions arranged hierarchicallywherein at least one of the microstructured patterns is suctional or thehierarchical combinations creates a suctional aspect. The surface 1300may consist of a flat substrate layer 1302 wherein on top of thesubstrate layer is embossed solid cylinders 1304. In some embodiments,the solid cylinders 1304 may be in a uniformly spaced square array. Ontop of each cylinder 1304 in the first pattern of cylinders may beembossed 1 to 10 solid cylinders of a smaller dimension 1306. Thesurface 1300 may also comprise interstitial areas between the firstlayer of cylinders 1304 wherein cylindrical holes 1308 may be disposedabout the bottom portion 1310 of the substrate layer 1302. Thesecylindrical holes may not communicate with the upper surface 1314, butmay stop between 5 and 20 microns before breaching the upper surface1314. Piercings 1316 may be disposed about the substrate layer 1302 suchthat each piercing may be aligned (or contiguous with) along the centeraxis 1318 of the holes 1308. The piercing 1316 may have a diameter ofbetween 1 to 10 microns. The fractal dimension of the cylindrical holes1308 may be in the range of 0.25 to 0.70. The capillary effect may beinitiated by placing the microstructure surface on the fluid layer ofthe target surface without any applied pressure. The first hierarchicalcylinders may draw water away from the target surface sufficiently thatthe water comes into contact with the pierced surface of the substratelayer. Then a slight pressure may be applied to the substrate 1300 andthe piercings 1316 act as valves to let fluid leave the interface layerthrough the cylindrical holes 1308, and not to return.

Thus, although there have been described particular embodiments of thepresent invention of a new and useful Patterned Surfaces with Suction itis not intended that such references be construed as limitations uponthe scope of this invention except as set forth in the following claims.

What is claimed is:
 1. A substrate having pressure-sensitive adhesion toa target surface, the substrate comprising: a surface with at least afirst microstructure pattern, a second microstructure pattern, and athird microstructure pattern, the first microstructure pattern includinga plurality of ridges, the second microstructure pattern comprising aplurality of micropillars, and the third microstructure patterncomprising a plurality of tiered columns; the surface having at least aportion wherein the first, second, and third microstructure patterns arearranged having the plurality of micropillars arranged in a plurality ofrows, the plurality of ridges disposed between and intersecting theplurality of micropillars, and wherein the plurality of tiered columnsare disposed adjacent the plurality of micropillars.
 2. The substrate ofclaim 1 wherein the plurality of ridges of the first microstructurepattern comprises a first set of latitudinal ridges and second set oflongitudinal ridges.
 3. The substrate of claim 1 wherein at least one ofthe plurality of micropillars of the second microstructure patterncomprise at least two latitudinal through-holes, each of the at leasttwo latitudinal through-holes having a latitudinal through-hole height,the latitudinal through-holes disposed about the at least onemicropillar, at least two longitudinal through-holes, each of the atleast two longitudinal through-holes having a longitudinal through-holeheight, and the longitudinal through-hole heights not equaling thelatitudinal through-hole heights.
 4. The substrate of claim 1 whereinthe plurality of micropillars further comprise a first set ofmicropillars and a second set of smaller micropillars wherein the firstset of micropillars and second set of micropillars are arrangedhierarchically such that the second set of micropillars is disposed on atop portion of the first set of micropillars.
 5. The substrate of claim1 wherein each of the plurality of micropillars is between 10 and 50microns in diameter, between 10 and 150 microns in height, and has apitch between 20 and 200 microns.
 6. The substrate of claim 1 whereineach of the plurality of tiered columns is between 10 and 50 microns indiameter, between 10 and 150 microns in height, and has a pitch between20 and 200 microns.
 7. The substrate of claim 1 wherein the plurality ofridges has a thickness between 5 and 50 microns, a height between 2 and150 microns, and a pitch between 5 and 50 microns.
 8. The substrate ofclaim 2 wherein the plurality of ridges are configured to generatecapillary action when in contact with liquid.
 9. The substrate of claim1 wherein at least a portion of the first microstructure pattern, thesecond microstructure pattern, or the third microstructure patterngenerates a Wenzel-Cassie state when in contact with a liquid.
 10. Thesubstrate of claim 1 wherein at least a portion of the firstmicrostructure pattern, the second microstructure pattern, or the thirdmicrostructure pattern generates a Cassie-Baxter state when in contactwith a liquid.
 11. The substrate of claim 1 wherein the surface is a topsurface, the substrate further comprises a bottom surface and aninterior between the top surface and the bottom surface; the interiorhaving a plurality of holes, each hole of the plurality of holes beingconnected with at least one of the top layer, the bottom layer, or both.12. The substrate of claim 11 wherein at least one hole of the pluralityof holes has a circumferential surface that is hydrophilic.
 13. Thesubstrate of claim 11 wherein at least one hole of the plurality ofholes has a circumferential surface that is hydrophobic.
 14. Thesubstrate of claim 3 wherein at least two latitudinal through-holes havea profile selected from the group consisting of circular, oval,rectangular, star, and polygonal.
 15. The substrate of claim 2 whereinthe latitudinal ridges comprise a plurality of individual ridgesoriented on a first axis, the longitudinal ridges comprise a pluralityof individual ridges oriented on a second axis, wherein the first axisis different from the second axis.
 16. The substrate of claim 15 whereinthe latitudinal ridges connect to the longitudinal ridges via theplurality of micropillars.